1. Field of the Invention
The invention relates to a positioning device with a mechanism for converting rotary motion into a linear motion, and more particularly, such a positioning device with a coarse adjustment and a fine adjustment.
2. Discussion of Relevant Art
German Patent DE 195 16 643 C1 describes a hardness testing equipment with an extending ram having a force measurement device at its tip. The ram can be moved in a two-stage manner by a combination with a spindle and a piezo positioner. The displacement movement can then be uncoupled by means of a spindle nut and a longitudinal guide integrated into the device. A movement of the piezo positioner is superposed on the movement of the spindle nut, in that the piezo positioner is coupled e.g. coaxially with the spindle nut. In this equipment, only the total stroke can be measured, and thus the reference surface is not clear. A measurement of a difference of the movement of the piezo positioner relative to the spindle nut is not provided. Since piezo elements operate with hysteresis, the deflection state of the piezo positioner therefore cannot be exactly given, particularly when a fine adjustment in the range of motion of e.g. 100.mu. is provided. A positioning movement takes place only in the axial direction. Since the equipment ends in a measuring tip for axial reaction forces, no transverse forces, which can arise from tilting of the sensed surface, need be taken up. Moreover, no alternating directions of motion are provided in the prior art equipment.
Japanese Laid-Open Patent Publication JP-A-8-313785 shows a microscope focusing drive with a conventional rack drive and a subsequent piezo element.